Method for manufacturing a gasket

ABSTRACT

A gasket for a bipolar battery comprises a structural part in the shape of a frame having an upper surface and a lower surface, and at least one channel to permit gas passage through the gasket. The structural part may be made from a first material having hydrophobic properties. The gasket further comprises at least a first sealing surface arranged in a closed loop projecting from the upper surface, and at least a second sealing surface arranged in a closed loop projecting from the lower surface. The first and the second sealing surfaces are provided on at least one sealing part, are made from a second material, and the first material of the structural part has a higher elastic modulus than an elastic modulus of the second material of the sealing parts. A bipolar battery and a method for manufacturing a gasket are also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This US non-provisional application is a Divisional of U.S. applicationSer. No. 11/889,201, filed Aug. 9, 2007, which is a Continuation-in-Partof U.S. application Ser. No. 10/712,018, filed Nov. 14, 2003, thecontent of both of which is incorporated herein by reference.

BACKGROUND

1. Technical Field

Example embodiments relate to a gasket, and a bipolar battery includingat least one gasket. Example embodiments also relate to a method formanufacturing a gasket.

2. Description of Related Art

A bipolar battery construction comprises an electrically conductivebipolar layer (or “biplate”) that serves as an electricalinterconnection between adjacent cells in the battery as well as apartition between the cells. In order for the bipolar construction to besuccessfully utilized, the biplate should be sufficiently electronicallyconductive to transmit current from cell to cell, chemically stable inthe cell's environment, capable of making and maintaining good contactto the electrodes, capable of being electronically insulated from otherbiplates, and sealable around the boundaries of the cell so as tocontain electrolyte in the cell.

The above characteristics are more difficult to achieve in secondary(rechargeable) batteries due to the charging potential that can generategas inside the battery, and in alkaline batteries due to the creepnature of the electrolyte. Achieving the proper combination of thesecharacteristics has proven very difficult.

A common type of battery design is the so called “flooded” batterywherein the electrolyte within the battery completely fills the porousspaces within the battery, with wet liquid electrolyte present in excessof that which can be absorbed by the constituent electrodes andseparators within the battery. More recent battery designs aredesignated as “starved electrolyte” or “recombinant” batteries. In thissort of battery design, the porous spaces within the constituentelectrodes and separators are not completely filled with electrolyte.Instead, some of this porous space is occupied by gases. As a result,the volume inside the battery surrounding the electrolyte issubstantially dry due to the remaining potential for the capillaryaction of the porous spaces to absorb wet liquid electrolyte. Thisresults in a battery configuration that is essentially damp, but notflooded or wet inside the battery. Such batteries have a volume intowhich gases generated within the battery can be contained. Starvedelectrolyte battery designs are typically much less tolerant of loss ofelectrolyte when compared to flooded batteries, as they have no extrawet reserve of electrolyte to compensate for electrolyte loss.Consequently, a starved electrolyte battery's internal volume is sealedfrom the ambient environment during normal use. It is common in the artto refer to starved electrolyte batteries as having a sealedconfiguration, as further described herein.

For maintenance-free operation it is desirable to operate rechargeablebatteries in a sealed configuration. However, sealed bipolar designstypically utilize flat electrodes and stacked-cell constructions thatpresent design challenges for proper containment of gases present andgenerated during cell operation. In a sealed construction, gasesgenerated during charging should be chemically recombined within thecell for stable operation. The pressure-containment requirement createsadditional challenges in the design of a stable bipolar configuration.

Technical fields such as transportation, communications, medical andpower tools (for example) are generating specifications that existingbatteries cannot meet. These include higher cycle life and the need forrapid and efficient recharges.

NiMH systems are seen as an alternative to meet cycle lifespecifications, but costs for existing conventional fabrication are toohigh.

In U.S. Pat. No. 5,344,723 to Bronoel et al., a bipolar battery isdisclosed having a common gas chamber, which is created by providing anopening through the biplate (conductive support/separator). The openingis also provided with a hydrophobic barrier to prevent passage ofelectrolyte through the hole. Although a problem with pressuredifferences between the cells may be avoided, there is still adisadvantage with the described battery. The outer sealing around theedge of each biplate still has to be fluid-tight, which is verydifficult to achieve. If the outer sealing is not fluid-tight, theelectrolyte, contained in the separator between the electrodes and inthe electrodes, may migrate and form a continuous ionic current leakagepath from one cell to another.

In U.S. Pat. No. 5,441,824 to Rippel, a quasi-bipolar battery isdisclosed where the structure of the battery attempts to addressproblems inherent when using the corrosive lead-acid chemical system ina bipolar configuration having biplates and separators. Here, thebiplate edges are encapsulated within a gas-tight continuous compliantframe material. The separator edges are also similarly encapsulated in agas-tight continuous complaint frame having gas passages formed intothem. Such encapsulation processes are expensive and difficult toaccomplish in a reliable, manufacturable fashion. The frame designdisclosed by Rippel has comparatively large areas present along thesealing surfaces. As a result, large forces are needed to cause therequired compressive strain in the disclosed frame necessary to induce agas tight seal. This large force must be borne by the structure of thebattery, resulting in larger size, higher weight and increased cost ofthe resulting battery. Rippel's disclosure also does not address theproblem of ionic currents that may flow in the electrolyte present inthe gas passages that can cause imbalanced self-discharge of individualbipolar electrodes in the battery.

The use of a common manifold for primary (non-rechargeable) reservebatteries to be activated in the field by filling of the electrolyteimmediately prior to use is well known in the art. In U.S. Pat. No.4,626,481 to Wilson discloses a flooded bipolar battery design using aprimary reserve activated Li/SOCl₂ system. This design comprises a frameencapsulating a biplate. This disclosure refers to this frame as an“insulating layer”. Again, such a continuous encapsulation is expensiveand more difficult to manufacture. Wilson addresses the problem ofreducing ionic currents that may flow in the electrolyte present in thegas passages by teaching use of a low conductivity electrolyte, which isclearly undesirable in a starved electrolyte secondary battery when highpower density is desired.

In the published international patent application WO 03/026042 A1,assigned to the present applicant, a hydrophobic barrier is introducedaround the electrodes instead of around the opening in the biplate (asdisclosed in U.S. Pat. No. 5,344,723). A pressure relief valve is alsointroduced to prevent a pressure build up inside the case. It is howeverrather expensive to manufacture a bipolar battery of this design inlarge quantities and therefore there is a need to construct a newbipolar battery having a smaller quantity of components, using simplerprocessing techniques to manufacture a bipolar battery.

In the published international patent application WO 2005/048390 A1,assigned to the present applicant, a bipolar battery design isdisclosed. The bipolar battery has a gasket made from a hydrophobicmaterial with a built-in gas passage arranged between adjacent biplates,wherein the gas passages within the gaskets create a common gas spacewithin the battery and at the same time electrolyte is prevented frommigrating between cells. However, a high degree of mechanical preloadedforce should be maintained over the gaskets to achieve these objectives,which in turn requires an outer casing that may withstand the stressthat will result from the force needed. Teaching of details regardingtop level construction resulting in a finished starved electrolytebipolar battery is found in this published international patentapplication WO 2005/048390 A1, which is incorporated here by reference.

SUMMARY

Example embodiments provide a gasket that will reduce the mechanicalpreloaded force needed over the gaskets to maintain a sealed gas space,and prevent wet electrolyte bridging that can allow ionic currents toflow between cells within a bipolar battery.

Example embodiments may implement a gasket with hydrophobic propertiesin the shape of a frame including a gas passage. The frame comprises atleast two parts, wherein a first part provides sealing and a second partprovides a mechanical structure. The material of the first part is moredeformable than the material of the second part. Put differently, thematerial of the first part has a lower elastic modulus than the materialof the second part.

According to example embodiments, the reduced facing area of thedeformed sealing surface when assembled into a battery results in lessrequired compressive force needed to maintain a seal.

According to example embodiments, a less rigid and lighter casing may beused to maintain a pressure tight seal and a common gas space within thebattery. This in turn reduces the weight of the completed bipolarbattery compared to prior art batteries.

Example embodiments provide additional cost and assembly benefitscompared to prior art devices.

According to example embodiments, a stack of gaskets within a bipolarbattery is more stable than a bipolar battery provided with prior artgaskets.

According to example embodiments, a better seal uniformity is achievedsince a more deformable part is providing the sealing.

The above and other features of example embodiments will become apparentto those skilled in the art from the following detailed description ofthe disclosed bipolar electrochemical battery and the biplate assembly.It will be understood that the details of example embodiments are shownby way of illustration only and not as limitations of the invention. Theprinciples and features of this invention may be employed in varied andnumerous embodiments without departing from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings are not to scale.

FIG. 1 is a plan view of a prior art gasket.

FIGS. 2 a and 2 b are cross-sectional views of the prior art gasket inFIG. 1.

FIGS. 3 a and 3 b are top and bottom plan views, respectively, of agasket according to an example embodiment of the present invention.

FIGS. 4 a and 4 b are cross-sectional views of the gasket in FIGS. 3 aand 3 b.

FIGS. 5 a and 5 b are top and bottom plan views, respectively, of agasket according to another example embodiment of the present invention.

FIGS. 6 a and 6 b are cross-sectional views of the gasket in FIGS. 5 aand 5 b.

FIG. 7 is a cross-sectional view of a bipolar battery according to anexample embodiment of the present invention.

FIG. 8 is a flow chart of a process for manufacturing a gasket accordingto an example embodiment of the present invention.

FIG. 9 is a top plan view of a gasket according to another exampleembodiment of the present invention.

FIGS. 10 a and 10 b are cross-sectional views of the gasket in FIG. 9.

DETAILED DESCRIPTION OF EXAMPLE, NON-LIMITING EMBODIMENTS

Benefits of the bipolar battery design include simplicity and lowresistance losses. The parts count of the battery is relative low, andmay consist only of endplates and biplates, with appropriate assembly ofelectrodes, separators and electrolyte and sealing components. Batteriesof a desired voltage are constructed by stacking the required number ofbiplates. The electrical connections between the cells are made as thebattery is stacked, since each biplate is electrically conductive andimpervious to electrolyte.

With terminals at each end of the stack, the flow of current isperpendicular to the plate, which ensures uniform current and voltagedistribution. Since the current path is very short the voltage drop issignificantly reduced.

Bipolar batteries will also have significantly reduced weight, volumeand manufacturing costs due to elimination of components and themanufacturing approach.

A problem with bipolar batteries is obtaining a reliable seal betweencells. Different solutions to this problem have been disclosed in thepublished international patent applications WO 03/009413, WO 03/026055and WO 03/026042, and in the published US applications US2004/0091784and US2005/0260493 (issued as U.S. Pat. No. 7,258,949), all of which areassigned to the present applicant, and hereby incorporated by reference.

The seal on a cell is of extreme importance for all types of batteries,and bipolar batteries are no exception. Individual cells contain theactive materials (for NiMH batteries, for example, it is Nickelhydroxide positive and metal hydride hydrogen storage alloy negative,respectively), separator and electrolyte. The electrolyte in theseparator is required for ion transport between the electrodes and theseparator provides insulation to the conduction of electronic currentflow between the electrodes. Designs, optimized for longevity, weightand volume, require recombination of gasses.

Batteries produce gasses as they are charged. The gassing rate increasesas the battery nears full charge, and reaches maximum when fullycharged. The gasses which are produced are primarily oxygen andhydrogen.

For Nickel based bipolar batteries, such as NiMH and NiCd, oxygen willrecombine relatively rapidly with available chemically active materialin the negative electrode. Batteries are normally designed so oxygenwill be the first gas generated if the cell is overcharged. Thisrequires two actions:

1) Overbuild the negative active material, generally by 30%, to ensurethat the positive electrode, which will gas oxygen on charge, will bethe first to gas.

2) In a starved electrolyte battery, provide for gas passage from thepositive to the negative, where the oxygen will recombine. The gaspassages are obtained by controlling the amount of electrolyte withinthe pores of the electrode and through the separator. The surfaces ofthe electrode must be covered by a thin layer of electrolyte for thetransport of ions, but the layer must be thin enough to permit gasdiffusion through the layer, and must allow gas passages throughout theactive layers and the separator.

The negative electrode alone would gas hydrogen if overcharged. Becausegaseous hydrogen does not recombine quickly, pressure would build upwithin the cell. If the rate of transport of oxygen across the cell fromthe positive electrode is not unduly impeded, then the oxygenrecombination effectively discharges the negative at the same rate it isbeing charged, thus preventing overcharge of the negative.

The surface area of the active material, the porosity of the electrode,and the presence of gas passages within the porous volumes in thebattery components enhance rapid recombination.

For clarity sake, a starved electrolyte battery is defined as is anessentially moist but not wet construction, as opposed to floodedbatteries like a typical lead acid car battery.

The bipolar approach helps ensure that the voltage drop across theactive material will be uniform in all areas, so that the entireelectrode across its facing area will come up to full charge at the sametime. This is due to the more uniform distribution of current densityacross the electrode face present in the bipolar approach. This helpsreduce the problem of inhomogeneous charge across the electrode areafound in many conventional constructions, where parts of an electrodeare overcharging and gassing while other (remote) areas of the electrodeare not yet fully charged.

The cells in regular batteries are sealed to contain the gases andelectrolyte both for proper performance of the cells, and to preventelectrolyte paths, i.e. continuous ionically conductive paths, betweenadjacent cells. The presence of electrolyte paths between cells willallow the electrodes of the electrolyte-connected cells to discharge ata rate that is determined by the resistance of the path (length of pathand cross section of path). The seals on bipolar batteries are moreimportant because the electrolyte path is potentially much shorter. Afeature of this disclosure is the use of a gasket with an integratedelectrolyte barrier to minimize or eliminate the conductivity of anypotential ionic conduction path. An additional concern is the amount ofheat generated by operation of the cell. Depending on the magnitude ofheat generated, the design must be able to reject the heat and maintaina safe operating temperature.

If an electrolyte path is developed between cells, a small intercellularleakage can be overcome by the periodic full charging of the battery.The battery may be overcharged by a set amount and at a low rate. Thelow rate would allow fully charged cells to recombine gasses withoutgenerating excessive pressure and also allow for easier conduction ofthe heat from the recombination/overcharge away from the battery. Cellsthat have small intercellular electrical leakage paths would becomebalanced.

It is rarely necessary that a battery be fully charged to achieve itsuseful function. Batteries are routinely over specified and overbuilt.If an application requires 50 AH (Ampere Hours), the requirement isusually specified at least 10% higher. Since batteries lose capacityover their lifetime, the capacity of a new battery is increased by theexpected loss, resulting in possibly a 70 AH requirement for a newbattery in this example. The manufacturer will probably have a mediandesign target of 75 AH to allow for variations in the manufacturingprocess. Some of this overbuild is to compensate for the life capacitydegradation that is caused by the overcharging.

A feature in the prior art bipolar batteries is the creation of a commongas space within the battery. The means for creating a common gas spacefor all cells in a bipolar battery comprises a gasket having apredetermined shape. The gasket is arranged between adjacent biplatesand/or a biplate and an end plate, as described below. The gasket ispreferably made with a thermoplastic elastomer compound that forms aseal with the biplate under pressure. One or more gas channels aremolded into the frame to ensure a continuous gas transmission path. Whenseveral gaskets are stacked upon each other a common gas space will becreated which will eliminate the pressure difference between the cellsin a bipolar battery. Note that such a common gas space is sealed fromthe ambient environment.

FIG. 1 shows a prior art gasket 10. The gasket 10 is manufactured in ahydrophobic material having deformable properties, such as an elastomeror other material that create a continuous seal when deformed, to beable to function as a sealing. The gasket has elastic properties, and asuitable material is a thermoplastic elastomer. Thermoplastic elastomersmay be obtained from several manufacturers e.g. Engage® 8407 availablefrom DuPont Dow Elastomers, DYNAFLEX® G2780-001 available from GLS Corp.or KRATON™ G-7705 available from Kraton™ Polymers. The gasket isinjection molded into the desired size and shape.

The gasket 10 is provided with a rim 11 at the edge on the upper surfaceand a corresponding indentation 12 on the reverse surface. The rim 11and the indentation 12 will provide alignment of the gaskets when theyare stacked upon each other in an assembled battery. The rim furtherserves to align the biplate relative to the gasket. The gasket isfurther provided with a through-hole 13 and a groove 14 to connect thethrough-hole 13 to the space on the inside of the gasket 10 when abiplate is mounted to the gasket. The through-hole 13 and the groove 14provide a gas channel between adjacent cells in the assembled battery,and the hydrophobic properties of the gasket prevent electrolyte fromcreating an ionically conductive path between adjacent cells. The gasketthus has four purposes when mounted:

1) prevent electrolyte from creating an ionically conductive path(leakage) between adjacent cells in a bipolar battery,

2) provide a gas channel between adjacent cells to create a common gasspace within a bipolar battery,

3) provide an outer pressure tight seal for the cells in a bipolarbattery, and

4) provide an electronically insulating support structure betweenbiplates and between the biplates and the endplates.

FIG. 2 a shows a cross-sectional view of the gasket taken along the lineA-A in FIG. 1, and FIG. 2 b shows a cross-sectional view of the gaskettaken along the line B-B in FIG. 1. The presence of a second gasket 10′is indicated in the figures to further show how the rim 11 is intendedto be received in the indentation when mounted in a battery.

A biplate 15 is shown with a dashed line in FIGS. 1, 2 a and 2 b toindicate the position of a biplate 15 in an assembled bipolar battery. Aportion of the groove 14 is covered by a biplate 15 to preventelectrolyte leakage between cells. A biplate with a hole aligned withthe hole in the gasket may alternatively be employed to serve thepurposes listed here.

FIG. 3 a is a top plan view of a gasket 20 according to an example,non-limiting embodiment. The gasket 20 comprises a structural part 27.In this example embodiment, the structural part 27 has an outer surface4 formed by a rim 21 that extends from an upper surface 1 and acorresponding indentation 22 on an opposed, lower surface 2, see FIG. 3b. The rim 21 and the indentation 22 will provide alignment of thegaskets 20 when they are stacked upon each other in an assembled bipolarbattery, as indicated in FIGS. 4 a and 4 b. The structural part 27 ofthe gasket 20 is provided with a through-hole 23 between the uppersurface 1 and the lower surface 2, and a groove 24 to create a passagefrom the through-hole 23 to an inner surface 3 of the structural part27, and thus the space contained inside the gasket 20 when a biplate 25is mounted on both upper 1 and lower 2 surfaces of the gasket. Thethrough-hole 23 and the groove 24 provide a gas channel between adjacentcells in the assembled battery. The biplate 25 is shown in phantom toindicate the position of the biplate 25 in an assembled bipolar battery.FIG. 3 b shows a bottom plan view of the gasket 20 in the regioncontaining section A-A in FIG. 3 a.

The gasket comprises in, this embodiment, two parts inclusive of thestructural part 27 and a sealing part 26. The sealing part 26 has moredeformable properties than the structural part 27. Thus, the materialused for the sealing part 26 has a smaller elastic modulus compared tothe material used for the structural part 27, which has a greaterelastic modulus. The structural part 27 is formed as a frame and acts asa reinforcement of the gasket 20 to provide a mechanical structure. Notethat the structural part 27 does not form a continuous encapsulation ofthe biplate 25, as is taught in some of the prior art.

The commonly denoted sealing part 26 is comprised of a first sealingpart 26 ₁ arranged in a closed loop on the upper surface 1 of thestructural part 27, and a second sealing part 26 ₂ arranged in a closedloop on the lower surface 2 of the structural part 27 and on the outsideof the hole 23, as indicated in FIGS. 3 a and 3 b. Furthermore, a thirdsealing part 26 ₃ is circumventing the hole 23 on the upper surface 1and is joined to the first sealing part 26 ₁. The first and the secondsealing parts 26 ₁ and 26 ₂ provide sealing that prevents electrolytefrom migrating between adjacent battery cells when mounted in a bipolarbattery. The third sealing part 26 ₃ shown in this embodiment isoptional and will enable vacuum filling the battery with electrolyte, ashas been disclosed in WO 2005/048390 A1, which is hereby incorporated byreference.

Each sealing part 26 has a sealing surface projecting from therespective surface of the structural part 27. Each sealing surfacecomprises a ridge 30 that extend along the closed loops. A recess 31 isprovided on each side of the ridge 30 along the closed loops. Thesealing is obtained by deforming the projecting surface, i.e. the ridge30, of each sealing part 26 against the biplate 25 or against thesurface of an adjacently arranged gasket as shown in FIGS. 4 a and 4 b.If recesses 31 are present, material from the ridge 30 will deform intothe recesses 31 when compressed.

The structural part 27 is preferably manufactured in one piece (i.e.,having a unitary one-piece construction), and the sealing part 26 ispreferably molded in one piece using an overmolding technique, asdescribed in more detail below. Regularly spaced openings 29 areprovided in the structural part 27 along the frame, and the sealing part26 is preferably injection overmolded onto the structural part 27 usingthese openings 29 to distribute the smaller elastic modulus materialused to create the first 26 ₁, the second 26 ₂, and optionally the third26 ₃ sealing part at the same time in a topologically connected manner.The technique of overmolding elastomeric materials onto more rigidsubstrates is well known in the art of plastic part manufacturing, andis not described in further detail here. It is of course possible tomanufacture one or more of the sealing parts individually in atopologically disconnected manner, as indicated in FIGS. 5 a, 5 b, 6 aand 6 b. These sealing parts are preferably formed onto the structuralpart 27 using injection molding, and may also be fabricated separatelyand assembled into a completed gasket 20. The structural part may bemanufactured using casting or machining, but is preferably injectionmolded before the sealing parts 26 are provided to complete the gasket20.

FIG. 4 a is a cross-sectional view along the lines A-A in FIGS. 3 a and3 b, and FIG. 4 b is a cross-sectional view along the line B-B in FIG. 3a. The presence of a second gasket 20′ is indicated in the figures toshow how the rim 21 is intended to be received in the indentation 22when mounted in a battery.

A biplate 25 is shown in phantom in FIGS. 3 a, 3 b, 4 a and 4 b toindicate the position of a biplate 25 in an assembled bipolar battery.The sealing surface, i.e. a portion of the ridge 30, at least on theupper surface 1 of the gasket 20, is configured to be positioned incontact with the biplate 25 to prevent electrolyte leakage between cellswhen mounted in a bipolar battery. A biplate with an opening alignedwith the hole 23 in the gasket 20 may alternatively be used to serve thepurposes listed above.

In this embodiment, locations of the first 26 ₁ and the second 26 ₂sealing parts are at least partially overlapping as projected onto animaginary plane parallel to the upper surface of the structural part ina direction perpendicular to the upper surface 1 of the structural part27. Thus, an offset “d” is present between the ridge 30 on the uppersurface 1 compared to the ridge 30 on the lower surface 2 of the gasket20. The reason for this is to ensure that both ridges 30 will bedeformed, either directly or indirectly via a biplate 25, against thestructural part 27 of an adjacent gasket 20′ as indicated in FIGS. 4 aand 4 b. In section A-A, only one ridge 30 is present on the left sideupper surface 1 since the groove 24 providing the gas channel is presenton the lower surface 2. The hydrophobic properties of the material usedfor the structural part 27 will ensure that a continuous ionic currentpath conducted by electrolyte through the gas channel is inhibitedbetween adjacent cells when mounted in a bipolar battery.

Thus, locations of the first 26 ₁ and the second 26 ₂ sealing parts arein this embodiment at least partially overlapping as projected onto animaginary plane parallel to the upper surface of the structural part ina direction perpendicular to the upper surface of the structural part27.

FIG. 5 a shows a top plan view, and FIG. 5 b shows a bottom plan view,of a gasket 40 according to another example embodiment of the presentinvention. Reference numbers indicating features described in connectionwith FIGS. 3 a and 3 b have been used to denote similar or identicalfeatures in FIGS. 5 a and 5 b. The gasket 40 comprises four partsinclusive of a structural part 44 and three separate sealing parts 41,42 and 43. The sealing parts 41, 42 and 43 have more deformableproperties than the structural part 44. Thus, the material used forsealing parts 41, 42 and 43 has a smaller elastic modulus than thematerial used for the structural part 44, which has a greater elasticmodulus. The structural part 44 is formed as a frame and acts as areinforcement of the gasket 40 to provide a mechanical structure, asdescribed in connection with FIGS. 3 a and 3 b.

A biplate 45 provided with an opening 46 aligned with the hole 23, whenplaced at a mounting position, is outlined in FIGS. 5 a, 5 b, 6 a and 6b with dashed lines. The first sealing part 41 is arranged in a closedloop on the upper surface 1 of the structural part 44. The secondsealing part 42 is arranged in a closed loop on the lower surface 2 ofthe structural part 44 and on the outside of the hole 23, as indicatedin FIGS. 5 a and 5 b. A third sealing part 43 is circumventing the hole23 on the upper surface 1. The purposes of the first, second and thirdsealing parts are the same as described above.

Each sealing part has a sealing surface projecting from the respectivesurface of the structural part 44. Each sealing surface comprises atapered ridge 47 that extends along the closed loop. The sealing isobtained by deforming the projecting surface, i.e. the ridge 47, of eachsealing part against the biplate 45, as shown in FIGS. 6 a and 6 b. Therim and the corresponding indentation may be omitted, as indicated inFIGS. 5 a, 5 b, 6 a and 6 b, if other means to align the gasket is used,such as arranging the gaskets in an appropriately designed casing, forexample.

The structural part 44 is in this embodiment preferably manufactured inone piece by casting, machining, or molding. Each sealing part 41, 42and 43 is separately molded, preferably injection molded, onto thestructural part 44. Each sealing part 41, 42 and 43 could also be formedin a separate manufacturing process and assembled later to form thegasket 40.

FIG. 6 a is a cross-sectional view along the line A-A in FIGS. 5 a and 5b, and FIG. 6 b is a cross-sectional view along the line B-B in FIG. 5a. The presence of a second gasket 40′ is indicated together with asection of a casing 49 in the figures to show that the gaskets may bealigned without a rim and indentation when mounted in a battery.

A biplate 45 is shown in phantom in FIGS. 6 a and 6 b to indicate theposition of a biplate 45 in an assembled bipolar battery. The projectingsurface, i.e. the tapered ridge 47, of the first sealing part 41 and thesecond sealing part 42 is configured to be positioned in contact with abiplate 45 to prevent electrolyte leakage between cells when mounted ina bipolar battery. An opening 46 in the biplate 45 is aligned with thehole 23 in the gasket 40 to serve the purposes listed above.

In this embodiment, locations of the first 41 and the second 42 sealingparts are non-overlapping as projected onto an imaginary plane parallelto the upper surface 1 of the structural part 44 in a directionperpendicular to the upper surface 1 of the structural part 44. Thus, anoffset “D” is present between the ridge 47 on the upper surface 1compared to the ridge 47 on the lower surface 2 of the gasket 40. Thereason for this is to ensure that both ridges 47 will be deformed,either directly or indirectly via a biplate 45, against the structuralpart 44 of an adjacent gasket 40′ as indicated in FIGS. 6 a and 6 b. Insection A-A, only one ridge 47 is present on the left side upper surface1 since the groove 24 providing the gas channel is present on the lowersurface 2. The hydrophobic properties of the material used for thestructural part 44 will ensure that the migration of electrolyte throughthe gas channel is prevented between adjacent cells when mounted in abipolar battery.

FIG. 9 shows a top plan view of a gasket 80 according to another exampleembodiment of the present invention. Reference numbers indicatingfeatures described in connection with previous embodiments have beenused to denote similar or identical features in FIG. 9. The gasket 80comprises two parts inclusive of a structural part 82 and a commonsealing part 81. The common sealing part 81 has more deformableproperties than the structural part 82. Thus, the material used for thesealing part 81 has a smaller elastic modulus than the material used forthe structural part 82, which has a greater elastic modulus. Thestructural part 82 is formed as a frame and acts as a reinforcement ofthe gasket 80 to provide a mechanical structure, as described inconnection with the previous embodiments.

The structural part 82 has an outer surface 4 formed by a rim 86extending from an upper surface 1, and a corresponding indentation 87 onan opposed, lower surface 2. The rim 86 and the indentation 87 willprovide alignment of the gaskets 80 as discussed in connection withFIGS. 3 a and 3 b. With reference to FIG. 10 a, the common sealing part81 of the gasket 80 is provided with a through-hole 83 between an uppersurface 91 and a lower surface 92, with a groove 84, to create a passagefrom the through-hole 83 to an inner surface 93 of the common sealingpart 81, and thus the space contained inside the gasket 80 when abiplate 85 is mounted on both upper 1 and lower 2 surfaces of the gasket80. The through-hole 83 and the groove 84 provide a gas channel betweenadjacent cells in the assembled battery. A biplate 85 is shown inphantom to indicate the position of the biplate 85 in an assembledbipolar battery.

The common sealing part 81 is provided with two sealing surfaces 91 and92. The upper sealing surface 91 extends in a direction away from andperpendicular to the upper surface 1 of the structural part 82, thus theupper sealing surface 91 projects from the upper surface 1. The lowersealing surface 92 extends in a direction away from and perpendicular tothe lower surface 2 of the structural part 82, thus the lower sealingsurface 92 projects from the lower surface 2. The common sealing part 81is preferably attached to an inner surface 90 of the structural part 82by molding and projections 88 may be provided on the inner surface 90 tofurther improve the bonding.

Preferably, the material used for the sealing parts also has hydrophobicproperties. A thermoplastic elastomer VERSAFLEX® CL2250 available fromGLS Corp. is a suitable material for the sealing parts, andpolypropylene, which is available from many suppliers, is a suitablematerial for the structural part. It is preferable that the materialchosen for the sealing parts be chemically compatible with theelectrolyte used. In an alkaline battery such as NiMH, compatibilitywith Potassium Hydroxide is typically required. This material shouldpreferably be chosen to have properties such as low compression set andlow creep.

It may be advantageous, but not necessarily required, to alter thedesign of the gasket in contact with the endplates to better nest andseal with the endplates. The endplates may have a different size thanthe biplates, so the gasket may need to conform to the different size.

This disclosure refers to the top and the bottom of gaskets as well asthe upper and the lower surfaces of gaskets and their constituent parts.It is understood that this terminology is used to describe the spatialrelationship of the parts relative to each other, and does not implythat neither the parts nor the battery that comprises them need beoriented in any special way relative to gravity for their assembly,function, or operation.

FIG. 7 shows, as a non-limiting example, a starved electrolyte bipolarbattery 50 in cross section having six cells arranged within a case 59.The battery comprises a negative end plate 51 and a positive end plate52, each having a negative electrode 53 and a positive electrode 54,respectively. Five biplate assemblies, comprising a negative electrode53 a biplate 25, and a positive electrode 54, are stacked on top of eachother in a sandwich structure between the two end plates 51 and 52,which are accessible from the outside. A separator 55 is arrangedbetween each adjacent negative and positive electrodes making up a cell,the separator 55 contains an electrolyte and a predetermined percentageof gas passages. About 5% is a typical value for gas passages in theporous volume of starved electrolyte batteries. The common gas manifoldremains essentially dry, containing a negligible amount of electrolyte,if any.

A gasket 20, as described in connection with FIGS. 3 a, 3 b 4 a and 4 b,is provided between adjacent biplates 25 and/or a biplate 25 and an endplate 51 or 52. As indicated in the figure by the arrow 56, gas may flowfrom one cell to another and thereby all cells share a common gas spacethrough the gas passages in the gasket. If an electrode in a cell startsto gas before the others, this pressure will be distributed through-outthe whole common gas space. The gas will pass from a cell, through agroove 24 and via a through-hole 23 of a first gasket to a groove 24 ofa second gasket, and thereafter into a second cell.

If the pressure within the common space exceeds a predetermined value, apressure relief valve 57 will open to connect the common gas space withthe ambient environment. The pressure relief valve 57 is arrangedthrough one of the end plates, in this example the positive end plate 52and comprises a feed-through 58. In an alternative embodiment, thefeed-through 58 may be integrally formed onto the endplate 52.

The purpose of the case 59 is to provide the mechanical preloaded forceneeded over the stacked gaskets 20 to maintain the sealed gas space.Note that a non-sealed case that provides a required mechanicalpreloaded force may be used to create an operational bipolar batterywith gaskets as described above. The gaskets described in connectionwith FIGS. 5 a, 5 b and 9 may naturally be used instead of the gaskets20 used in the bipolar battery 50.

FIG. 8 shows a flow chart for manufacturing a gasket according to anexample embodiment of the present invention. The process start at step60, and if the gasket is selected to be manufactured in more than twosteps in step 61, the flow continues to step 62. A structural part ismanufactured in step 62, in the shape of a frame from a first materialhaving hydrophobic properties. A gas channel is provided through thestructural part between upper and lower surfaces, and an inner surfaceof the structural part, and the gas channel is preferably provided onlythrough the structural part. The first material preferably has anelastic modulus sufficiently high to provide a rigid structure.

The flow continues to step 63, wherein an integer k is set to 1 (k=1)and a variable n is set to the number of sealing parts desired, e.g. twoseparate parts (n=2). If the gasket is to be manufactured from separateparts, the flow proceeds to step 65 via step 64. A first sealing part ismanufactured in step 65 from a second material having a lower elasticmodulus compared to the elastic modulus of the first material. The firstsealing part is manufactured in a closed loop, and the second materialpreferably has hydrophobic properties. If n≠k in step 66, then the flowis fed back to step 65 via step 67 in which the integer k is increasedby one, i.e. k=k+1. A second sealing part is thereafter manufactured inthe repeated step 65 and the steps are repeated until n=k in step 66,and then the flow continues to step 68. The gasket is assembled in step68 by arranging the separate sealing parts to the structural part insuch a way that the closed loop of at least the first and a secondsealing part are arranged along the frame on opposite surfaces of thestructural part. The gasket is completed and the flow ends in step 69.

If a decision not to make separate parts is taken in step 64, the flowcontinues to step 70 in which the first sealing part is molded,preferably injection molded, from a second material on a surface of thestructural part. If n≠k in step 71, then the flow is fed back to step 70via step 72 in which the integer k is increased by one, i.e. k=k+1. Asecond sealing part is thereafter molded, preferably injection molded,to the structural part in the repeated step 70 and the steps arerepeated until n=k in step 71. The gasket is then completed and the flowends in step 69.

On the other hand if the gasket is selected to be manufactured in onlytwo steps in step 61, the flow continues to step 73 wherein a decisionis made whether a common sealing part is to be used. If a common sealingpart is to be used, a structural part is manufactured in step 74, in theshape of a frame from a first material preferably having hydrophobicproperties. The flow will continue directly to step 75 to mold thecommon sealing part to the structural part. The common sealing part madefrom a second material having a lower elastic modulus compared to theelastic modulus of the first material is provided in a closed loop alonginner surface of the structural part. The sealing part is made in amolding process, preferably an injection molding process, and the secondmaterial has hydrophobic properties since a gas channel is providedthrough the common sealing part. The gasket is then complete and theflow ends in step 69.

On the other hand, if several sealing parts are to be used the flowcontinues to step 76 where a structural part is manufactured in theshape of a frame from a first material having hydrophobic properties.Openings are also provided along the frame of the structural part instep 76. A gas channel may also be provided through the structural partbetween upper and lower surfaces, and an inner surface of the structuralpart, and the gas channel is preferably provided only through thestructural part. The first material preferably has an elastic modulussufficiently high to provide a rigid structure.

The flow continues to step 77, in which at least sealing parts made froma second material having a lower elastic modulus compared to the elasticmodulus of the first material are simultaneously provided in closedloops along the frame at least on an upper and lower surface of thestructural part. The sealing parts are made in a molding process,preferably an injection molding process, and the second materialpreferably has hydrophobic properties. Other parts may also be moldedsimultaneously, e.g. circumscribing the hole of the gas channel in thestructural part. The openings in the structural part provide thepossibility to simultaneous mold the sealing parts in an overmoldingprocess. The gasket is then complete and the flow ends in step 69.

The structural part is preferably manufactured in an injection moldingprocess, but may be manufactured using other types of techniques, suchas machining and casting.

What is claimed is:
 1. A method comprising: a) creating a structuralpart in the shape of a frame and having an upper surface and a lowersurface, the structural part being made from a first material; b)attaching a first sealing part to the structural part, such that thefirst sealing part projects beyond the upper surface to provide at leasta first sealing surface arranged in a closed loop, the first sealingpart being made from a second material; c) attaching a second sealingpart to the structural part, such that the second sealing part projectsbeyond the lower surface to provide at least a second sealing surfacearranged in a closed loop, the second sealing part being made from thesecond material; d) selecting at least one of the first material and thesecond material to have hydrophobic properties; e) selecting the firstmaterial to have a higher elastic modulus than the second material; andf) creating at least one channel through the gasket.
 2. The methodaccording to claim 1, wherein the first sealing part and the secondsealing part are provided as a single, common sealing part; wherein thechannel extends through the common sealing part; and wherein the secondmaterial has hydrophobic properties.
 3. The method according to claim 1,wherein the channel extends through the structural part.
 4. The methodaccording to claim 1, wherein an injection molding process is used toattach the first and the second sealing parts to the structural part. 5.The method according to claim 1, wherein the structural part is madethrough an injection molding process.
 6. The method according to claim1, wherein the first sealing part and the second sealing part areprovided as a single, common sealing part attached to an inner surfaceof the structural part.
 7. The method according to claim 6, wherein thestructural part is provided with projections on the inner surface. 8.The method according to claim 1, wherein the first sealing part and thesecond sealing part are spaced apart from each other.
 9. The methodaccording to claim 8, wherein each of the first and the second sealingsurfaces comprises a ridge provided along the closed loops of the firstand the second sealing parts.
 10. The method according to claim 9,wherein a recess is provided on each side of the ridge along the closedloops of the first and the second sealing parts.
 11. The methodaccording to claim 1, wherein at least one opening is provided betweenthe upper and the lower surfaces of the structural part; and wherein thefirst sealing part and the second sealing part are injection molded onthe structural part simultaneously through the at least one opening. 12.The method according to claim 11, wherein multiple openings are providedalong the structural part.
 13. The method according to claim 1, whereinlocations of the first and the second sealing parts are at leastpartially overlapping as projected onto an imaginary plane parallel tothe upper surface of the structural part in a direction perpendicular tothe upper surface of the structural part.
 14. The method according toclaim 1, wherein locations of the first and the second sealing parts arenon-overlapping as projected onto an imaginary plane parallel to theupper surface of the structural part in a direction perpendicular to theupper surface of the structural part.
 15. The method according to claim1, wherein the first material has hydrophobic properties.
 16. The methodaccording to claim 1, wherein the gasket is made through an overmoldinginjection molding process.